The present work deals with two general areas of vagal control of breathing: 1. Response of Respiratory Phase Switching Mechanisms to Vagal Stimulation: This is a part of a broad project which aims to define the response characteristics of the switching mechanisms by examining the changes in their excitability during and following well-controlled inputs from different sources, i.e. vagal, intercostal, sympathetic, pontine and somatic inputs. The studies are done primarily in pentobarbital anesthetized cats. 2. Role of Vagal Volume Related Feedback in the Control of Breathing Pattern in Man: In the first stage of this project we have identified the presence of an important vagal modulation of breathing pattern in some subjects with normal lungs. In the next phase the study will be continued in patients with specified cardio-pulmonary disorders. These studies are done using the technique of airway occlusion, along with the recording of electrical activity of the diaphragm. The subjects are studied when unconscious either as a result of spontaneous medical reasons or of enflurane anesthesia given in the course of elective surgery.